In a stand mixer, fitted with the dough blade, add the butter and sugar and mix until light and fluffy, about 6 minutes. Add in the yolks, 1 at a time, then add the vanilla and combine well. Remove the bowl from the mixer and gently fold in the flour. Stir in the cold water, 1 tablespoon at a time, until the dough just comes together. Wrap in plastic wrap and refrigerate for 1 hour.
Lemon Curd: In a double boiler over medium-high heat, add all of the custard ingredients and whisk constantly until the mixture thickens and reaches 160 degrees F on an instant-read thermometer. Remove from heat and strain through a fine mesh strainer into a bowl. Cover the bowl, pressing plastic wrap onto the top of the custard and refrigerate until cool, about 1 hour.
Preheat the oven to 325 degrees F.
Remove the dough from the refrigerator and let it rest for 15 minutes (less if it is a hot day). Roll out on a silicone mat to 1/8 to 1/4-inch thick. Cut and press into the tart pans. Chefs Note: You can cut shapes out of the scraps to decorate or nibble on. Just brush the shapes with egg wash, sprinkle with a little tubinado sugar and bake until golden, about 10 minutes.
Prick the bottom of the tarts with a fork and refrigerate for 15 minutes.
Put the tarts on a baking sheet and bake until golden brown, about 15 to 20 minutes. Cool before filling.
If using, whip the heavy whipping cream in a large bowl until stiff peaks form.
Fill the shells with about 3 tablespoons of the curd and arrange fruit as desired on top. Garnish with a small dollop of the whipped cream and serve immediately. Can be made 20 to 30 minutes in advance and kept in refrigerator.